Production of an air product in an air separation plant with cold storage unit

ABSTRACT

A method for producing an air product in an air separation plant. Feed air is cooled at least in a main air compressor and is fed into a distillation column system. A fluid storage unit and a cold accumulator are used. In a first operating mode, fluid is stored in the fluid storage unit and the cold accumulator is heated. In a third operating mode, fluid is released and the cold accumulator is cooled, and in a second operating mode, fluid is neither stored nor released.

The invention relates to a process for producing an air product in an air separation plant and to a corresponding air separation plant according to the independent patent claims.

PRIOR ART

The production of air products in a liquid or gaseous state by cryogenic separation of air in air separation plants is known, and is described for example by H.-W. Häring (editor) in Industrial Gases Processing, Wiley-VCH, 2006, in particular section 2.2.5, “Cryogenic Rectification”. The present invention is particularly suitable for air separation plants with internal compression, as explained loc. cit., section 2.2.5.2, “Internal Compression”.

Air separation plants have distillation column systems, which may be designed for example as two-column systems, in particular as classic Linde double-column systems, but also as three- or multi-column systems. Apart from the distillation columns for producing nitrogen and/or oxygen in a liquid and/or gaseous state (for example liquid oxygen, LOX, gaseous oxygen, GOX, liquid nitrogen, LIN and/or gaseous nitrogen, GAN), that is to say the distillation columns for nitrogen-oxygen separation, distillation columns for producing further air components, in particular of the noble gases krypton, xenon and/or argon, may be provided.

For example, it is known from DE 31 39 567 A1 and EP 1 989 400 A1 to use liquid air or liquid nitrogen for grid control and provision of control capacity in electric power grids. At times of a high electricity supply (referred to hereinafter as times when there is a surplus of electric power), the liquid air or the liquid nitrogen is produced in an air separation plant with an integrated liquefier or in a dedicated liquefaction plant and stored in a system of tanks comprising low-temperature tanks. At times of a low electricity supply (referred to hereinafter as times when there is a shortage of electric power), the liquid air or the liquid nitrogen is removed from the system of tanks, the pressure is increased by means of a pump and it is warmed up to approximately ambient temperature or above, and is thereby transformed into a gaseous or supercritical state. In an energy storage unit, a pressurized stream thereby obtained is expanded to ambient pressure in an expansion turbine or a number of expansion turbines with intermediate heating. The mechanical power thereby released is transformed into electrical energy in one or more generators of the power generating unit and is fed into an electric grid.

The present invention is not so much concerned with the area of simply storing energy, but rather seeks to provide an energy separation plant in which air products, in particular internally compressed pressurized nitrogen and/or pressurized oxygen, are provided, advantageously in a comparable amount, both in times when there is a surplus of electric power and in times when there is a shortage of electric power. At the same time, however, the lower electricity prices in the times when there is a surplus of electric power are to be used and the higher electricity prices in the times when there is a shortage of electric power are to be avoided.

DISCLOSURE OF THE INVENTION

This object is achieved by a process for producing an air product in an air separation plant and a corresponding air separation plant according to the preambles of the independent patent claims. Refinements are the subject of the independent patent claims and the description that follows.

Before the features and advantages of the present invention are explained, the principles on which it is based and the terms used are explained. The devices explained are also described in the relevant specialist literature, for example loc. cit., section 2.2.5.6, “Apparatus”. Unless the following definitions use different terms, reference is expressly made to the specialist literature for the terminology that is used here.

A “heat exchanger” serves for the indirect transfer of heat between at least two streams that are for example made to flow counter to one another, for example a warm stream of compressed air and one or more cold streams or a cryogenic liquid air product and one or more warm streams. A heat exchanger may be formed by a single or multiple heat exchanger portions that are connected in parallel and/or in series, for example one or more plate heat exchanger blocks. It may for example be a plate heat exchanger (plate fin heat exchanger). Such a heat exchanger, for example also the “main heat exchanger” of an air separation plant, by which the main fraction of the fluid to be cooled down or to be warmed up is cooled down or warmed up, has “passages”, which are designed as fluid channels that are separate from one another and have heat exchanging surfaces and are interconnected separately by other passages to form “groups of passages”.

A “cold storage unit” serves for storing the thermal energy in the form of cold, that is to say extracted heat energy. For use in the context of the present invention, cold storage units may be structurally designed in particular in a way similar to the regenerators that are known in principle from the area of air separation plants. Regenerators are explained for example by F. G. Kerry, Industrial Gas Handbook, CRC Press, 2006, in particular sections 2.7, “Kapitza Cycle” and 4.4.3, “Recovery of Krypton and Xenon”. Regenerators comprise a material that is suitable for storing cold, in the simplest case for example a stone filling, which during the first time period is flowed through by a cold fluid, in particular a cryogenic fluid, and thereby cools down. During the second time period, a corresponding regenerator is flowed through by a warm fluid, which cools down on account of the cold stored in the regenerator or transfers its heat to the regenerator. Regenerators may also be used in air separation plants for cleaning the air that is used particularly of carbon dioxide and hydrocarbons that freeze or liquefy in the cooled-down regenerator and are vaporized or sublimated during the heating up of the regenerator. In a separation plants of a classic type, corresponding regenerators are typically operated in an alternating mode, in each case with a first generator or first group of generators being regenerated and a second regenerator or a second group of regenerators being on standby for cooling down or purifying the feed air.

As mentioned above, although cold storage units can be designed in a way similar to the regenerators, in chemical engineering terms the differences between these process units are great. These differences are explained below:

-   -   1. A regenerator primarily has the function of a heat exchanger,         that is to say it serves for transferring the heat from a warmer         stream of substance to a colder stream of substance. In an air         separation process, at least two generators are therefore always         required: the warmer stream is passed through one and the colder         stream is passed through the other. Thus, in chemical         engineering terms, a pair of regenerators may in principle be         replaced by a single conventional heat exchanger. If         regenerators are taken out of operation, the air separation         plant is no longer operational.         -   By contrast, the main function of a cold store is that of             storing the cold for a longer time, of example more than 30             minutes. In principle, a cold store cannot be replaced by a             heat exchanger. The cold store is often used as a single             cold store. If the cold store is not in operation, the air             separation plant can in principle continue to run             unproblematically.     -   2. The regenerator has in principle only two operating phases:         -   first, a cold gas portion is passed through the regenerator             and warmed up there (the regenerator is cooled), generally             for less than ten minutes.         -   after that, the regenerator is flowed through in the             opposite direction by the warm gas, which is thereby cooled             down (the regenerator is warmed up), generally for less than             ten minutes.         -   A cold store has at least three operating phases:         -   putting-into-storage phase: the cold store is first cooled             down by a cold gas; this generally takes longer than one             hour,         -   storing phase: the cold store subsequently remains cold over             relatively long times and is not flowed through,     -   removing-from-storage phase: the cold store is flowed through by         a warm gas and is warmed up (the gas is thereby cooled); this         generally takes longer than one hour,         -   this may be followed again by a rest phase, which may also             take several hours and in which the cold store is not flowed             through.     -   3. Other thermodynamic parameters are also different:         -   the average local change in temperature in a regenerator is             less than 10 K,         -   a cold store is internally warmed up or cooled down on             average by about 50 K, at least by 30 K.

Cold stores may also comprise corrugated aluminum sheets or concrete blocks permeated with channels (unusual in the case of air separation plants, but possible) in a way similar to heat stores. Such heat stores are extensively described in the relevant specialist literature. Suitable for example as storage media, as mentioned, are stone and concrete, but also brick, artificially produced ceramics or cast iron. For low storage temperatures, earth, gravel, sand and/or crushed rock can also be used.

An “expansion turbine” or “expansion machine”, which may be coupled to further expansion turbines or energy converters such as oil brakes, generators or compressors by way of a common shaft, is designed for the expansion of a gaseous or at least partially liquid stream. In particular, for use in the present invention, expansion turbines may be designed as turbo expanders. If a compressor is driven by one or more expansion turbines, but without energy that is externally supplied, for example by means of an electric motor, the term “turbine-operated” compressor or alternatively “booster” is used. Arrangements comprising turbine-driven compressors and expansion turbines are also referred to as “booster turbines”.

An “air product” is any product that can be produced at least by compressing and cooling down air and in particular, but not necessarily, by subsequent low-temperature rectification. In particular it may be liquid or gaseous oxygen (LOX, GOX), liquid or gaseous nitrogen (LIN, GAN), liquid or gaseous argon (LAR, GAR), liquid or gaseous xenon, liquid or gaseous krypton, liquid or gaseous neon, liquid or gaseous helium, etc., but also for example liquid air (LAIR). The terms “oxygen”, “nitrogen” etc. also refer here respectively to cryogenic liquids or gases which comprise the respectively mentioned air component in an amount that lies above that of atmospheric air. Therefore, they do not necessarily have to be pure liquids or gases with high contents.

In the context of the present application, an “air product” is also understood as meaning a corresponding fluid that is finally discharged from the air separation plant, that is to say is no longer used for expansion, evaporation, liquefaction, compression etc. in the air separation plant or subjected to a corresponding step. On the other hand, fluids produced by compressing and cooling down air, and in particular, but not necessarily, by subsequent low-temperature rectification, that are only intermediately stored or temporarily available but subsequently further treated in the air separation plant are referred to here as “intermediate products”. An intermediate product in the sense of this application is in particular a cryogenic liquid produced from air that is pressurized in a liquid form in the course of an internal compression process and subsequently warmed up in the main heat exchanger of an air separation plant.

As mentioned at the beginning, air separation plants may be operated with so-called internal compression. For details, reference should be made to the cited specialist literature. In the internal compression, a stream pressurized in a liquid form is warmed up and thereby transformed from the liquid state into the gaseous supercritical state, depending on which pressure the liquid stream was subjected to.

Hereinafter, the collective term “vaporization” is used for the transformation from the liquid state to the supercritical or gaseous state. The transformation from the supercritical gaseous state to the liquid state, the product of which is a clearly defined liquid, is referred to as “liquefaction”.

Advantages of the Invention

The present invention is based on a process for producing an air product in an air separation plant in which feed air, which is altogether compressed in a main air compressor and thereafter partly recompressed in a booster air compressor, is cooled down and subsequently entirely or partially fed into a distillation column system. The compressed air fed into the distillation column system of the air separation plant may in this case be the entire feed air compressed in the main air compressor, but it may also be envisaged only to feed a fraction of the feed air compressed in the main air compressor into the distillation column system and to expand a fraction, just for covering the cold demand of the air separation plant, and not feed it into the distillation column system, for example blow it off to the surrounding vicinity.

The process comprises three operating modes, the first operating mode being carried out during the times explained at the beginning when there is a surplus of electric power, the second operating mode being carried out during the times explained at the beginning when there is a shortage of electric power. Apart from these three mentioned operating modes, further operating modes may also be provided, as explained in more detail with reference to the accompanying FIGS. 2 to 4.

In the first operating mode, which as explained is carried out during the times when there is a surplus of electric power, the feed air is fed in a first air feeding amount into the distillation column system, and in this system the feed air is used to produce a liquid intermediate product in a first amount of intermediate product. The liquid intermediate product may be in particular liquid nitrogen, liquid oxygen and/or argon, that is to say fluids that can be used for example in an internal compression process for providing corresponding gaseous pressurized products. Liquid air may also serve as an intermediate liquid product. A corresponding amount may also be drawn off upstream of the distillation system, from the so-called throttle stream, or be removed from the distillation column system at one or more corresponding points of the low-pressure or high-pressure column.

Of the amount of intermediate product, one fraction is stored in a liquid form in a storage amount in a liquid storage unit, another fraction may be surrendered as a product to customers and a further fraction may be warmed up under pressure in a first amount of product in the main heat exchanger and provided as the air product to be produced. The warming up in the main heat exchanger under pressure is in this case advantageously performed with vaporization in the course of an internal compression process, as explained above.

The liquid storage unit used advantageously comprises one or more storage tanks for the liquid intermediate product or products. It should be emphasized that the process according to the invention is not restricted to the production of a single intermediate product; the process may also comprise the production of a number of intermediate products and their storage and/or provision as air products. The invention is described below on the basis of only one intermediate product or only one corresponding air product.

In the second operating mode, the liquid is stored and kept in the liquid storage unit, in principle without the level of the liquid being changed by adding or drawing off liquid intermediate product (As a departure from this principle, at most part of the stored liquid may be drawn off directly as liquid product if there is a demand for it at the time.) The air separation plant runs in the normal mode. The cold store is not flowed through.

In the third operating mode, which, as explained, is carried out during the times when there is a shortage of electric power, the feed air is fed in a third air feeding amount into the distillation column system and in this system once again the feed air is used to produce a liquid intermediate product in a third amount of intermediate product.

Furthermore, in the third operating mode, the liquid intermediate product stored in the first operating mode is removed in a removal amount from the liquid storage unit and combined with the third amount of intermediate product to form a total amount. The total amount forms a third amount of product, which is warmed up under pressure in the main heat exchanger and provided as the air product.

Another slightly different way of carrying out the process is also possible, one in which the liquid intermediate product stored in the first operating mode is removed from the liquid storage unit and first returned into the column system and combined there with the third amount of intermediate product to form a total amount.

In the case of liquid air as the liquid intermediate product, this liquid air is returned at the top into the column system, separated there into liquid oxygen and liquid nitrogen, and the liquid products produced are combined with the third amount of intermediate product to form a total amount.

Operating modes 1 and 3 consequently differ in particular in that in the first operating mode a corresponding liquid intermediate product is stored in the liquid storage unit and this intermediate product is removed again from the liquid storage unit in the third operating mode. While in the first operating mode a greater amount of intermediate product of the liquid intermediate product is produced than is required as an amount of product in the first operating mode, the amount of intermediate product in a third operating mode is much smaller, the smaller amount of intermediate product then be made up by the removal amount from the liquid storage unit. This makes it possible to operate the air separation plant in the third operating mode with significantly reduced operating costs, i.e. significantly reduced consumption of electrical energy.

The process according to the invention is consequently also distinguished by the fact that the first air feeding amount is greater than the second air feeding amount and the second air feeding amount is greater than the third air feeding amount. According to the invention, furthermore, in the first operating mode heat is extracted from the feed air both by using a cold storage unit that is cooled down in the third operating mode and comprises at least one cold store and by using the main heat exchanger. The present invention therefore not only envisages cooling down the feed air in the air separation plant only by means of a main heat exchanger or only by means of a cold storage unit, as respectively known in principle, but rather more, as also still to be explained in detail below, that the greater air feeding amount is additionally cooled by means of the cold storage unit in the first operating mode and the cold storage unit is cooled by means of cold available in surplus in the third operating mode. The cold is available in surplus in the third operating mode because the same or comparable amounts of air products are advantageously removed overall from the air separation plant, and consequently the same or a comparable amount of cold is available. However, the air feeding amount is smaller in the third operating mode. An essential aspect of the invention is that, in the first and third operating modes, the first and third amounts of product are indeed passed through the main heat exchanger, but not through the cold storage unit.

It is known that the cost-effectiveness of almost every air separation plant can be increased by adapting production to the power or energy tariff. Energy-expensive products such as liquids or high-pressure gases are increasingly produced when the power or energy is cheap; the production of such products is correspondingly throttled when the power or energy is expensive. The precondition for success of this strategy is that the user or customer of corresponding products is able and willing to adapt to the continually changing amounts of product. In practice, this precondition is only satisfied very rarely; for example, large chemical works or steelworks cannot control their production to any appreciable extent in dependence on power tariffs. The process according to the invention offers the particular advantage here of a constant amount of production, which nevertheless makes selective adaptation to the respective power or energy tariff possible.

The measures according to the invention therefore bring their advantages to bear in particular whenever the first amount of product does not differ from the third amount of product The difference existing in the context of the present invention advantageously only relates to the amounts fed in: in the third operating mode, a significantly smaller air feeding amount into the distillation column system is required and the cold demand is correspondingly lower. In the first operating mode, the air feeding amount is correspondingly greater, so that there is a correspondingly greater cold demand. The corresponding surplus of cold in the third operating mode and the greater cold demand in the first operating mode are balanced out by the cold storage unit provided in addition to the main heat exchanger. In the main heat exchanger itself, the feed air, or the fraction of the feed air that is passed through the main heat exchanger, is cooled down in counterflow to cold streams, as known to this extent. The extraction of the heat by using the cold storage unit in the first operating mode does not have to take place directly here, i.e. the feed air need not necessarily itself be passed through the cold storage unit. Rather, it is also possible to pass other streams through the cold storage unit, transfer their heat to the cold storage unit and then pass this through the main heat exchanger.

When in the context of this application mention is made of an “amount”, this should be understood in particular as meaning an amount per unit of time (in particular a mass flow).

The present invention advantageously makes it possible to provide the first air feeding amount greater by at least 20% than the third air feeding amount and the first amount of intermediate product greater by at least 20% than the third amount of intermediate product. Corresponding differences are entered directly into the calculation of the cost-effectiveness of a corresponding plant, because they are directly reflected in the required power costs. By contrast, the first and third amounts of product are preferably the same or differ by less than 5%.

Advantageously, a fraction of the feed air compressed in the main air compressor is recompressed in a booster air compressor amount, the booster air compressor amount being greater in the first operating mode than in the third operating mode. Apart from the savings in the operation of the main air compressor, which result directly from the reduction in the third air feeding amount in comparison with the first air feeding amount, in the context of the present invention the required electrical energy for the booster air compressor can therefore also be reduced. This once again results from the use of the cold storage unit cooled down in the third operating mode, which in this third operating mode can transfer heat to the streams to be warmed up here, in particular to the third amount of product of the air product that is made up of the third amount of intermediate product and the removal amount. The amount of a throttle stream otherwise required for an internal compression process, that is to say a stream of compressed air that is provided under high pressure and passed through the main heat exchanger with at least partial liquefaction, in order to be able to transfer heat for vaporization to a correspondingly pressurized liquid stream, can in this way be significantly reduced.

Additional production of cold by means of a turbine stream is also not required, or only to a lesser extent, in the third operating mode, because in the third operating mode no liquid intermediate products are stored, but instead cold is available on account of the (additional) removal amount of the intermediate product from the liquid storage unit. In this way, a reduction of a turbine stream, possibly to a minimal value or zero, is made possible, as also extensively explained in the description of the figures. The power of the booster air compressor is thereby further reduced correspondingly.

In other words, it is therefore particularly advantageous if, at least in the first operating mode, a fraction of the booster air compressor amount is cooled down in a turbine stream amount to a temperature level that lies above the liquefaction temperature of nitrogen, and is expanded in an expansion machine, and if a fraction of the booster air compressor amount is cooled down in a throttle stream amount to a temperature level that lies below the liquefaction temperature of nitrogen, and is expanded. The use of the corresponding streams as a throttle stream or turbine stream is known in principle from the specialist literature cited at the beginning.

Advantageously, the sum of the turbine stream amount and the throttle stream amount may be provided as greater in the first operating mode than in the third operating mode (or smaller in the third operating mode than in the first operating mode), which has the consequence of the mentioned energy savings in the third operating mode. The present invention makes it possible in particular to reduce to the greatest extent the compression power required for providing the turbine stream in the third operating mode, which is carried out during the times when there is a shortage of electric power. A corresponding booster air compressor or corresponding stages of such a booster air compressor can be operated at minimal rotational speed, which lowers the electric power consumption. As also explained with respect to the figures, the throttle stream can also be corresponding reduced.

Advantageously, after expansion, the throttle stream amount and the turbine stream amount are fed into the distillation column system as part of the air feeding amount, but it may also be envisaged to blow off fractions thereof, for example into the atmosphere, to use them for purposes of regeneration, etc.

The invention may also be used in a process in which part of the feed air that is not compressed in the booster air compressor is expanded by way of an expansion turbine into a low-pressure column of the distillation column system. Such processes may for example comprise feeding corresponding feed air into the low-pressure column by means of a so-called injection turbine.

It is particularly advantageous if the cold storage unit used in the context of the present invention comprises at least one cold store that is designed in the way explained above. In the context of the invention, it may also be envisaged to use a number of cold stores, one of which is used for the actual cold storage and the other is used for balancing the main heat exchanger used, that is to say for balancing surplus or reduced amounts of heat or cold and/or for influencing the corresponding heat exchange diagrams.

The cooling down of the cold storage unit, in particular a cold storage unit with at least one cold store, can be performed in the third operating mode in various ways, depending on how a corresponding cold store is designed. It may for example be advantageous to remove from the distillation column system a cryogenic gas product, in particular so-called impure nitrogen, a fraction of which is passed through the cold storage unit in the cryogenic state in the third operating mode to cool the unit down. This is therefore a cryogenic gas product that is not provided in the form of a first or third amount of product, but is an additional product. A further fraction of the cryogenic gas product may be passed through the main heat exchanger and cool down further streams or fractions of the feed air in counterflow there. The cryogenic gas product is removed in particular from the low-pressure column of a corresponding distillation column system and is therefore at a corresponding pressure, for example at 1.4 bar.

It may be envisaged to warm up the cryogenic gas product completely in the main heat exchanger, a fraction of which is passed through the cold storage unit in the cryogenic state in the third operating mode to cool the unit down, a fraction of the warmed-up gas product being passed through the cold storage unit to warm the unit up. This variant of the process according to the invention may be carried out in particular by forming a recycle stream, which branches off at the warm end of the main heat exchanger from a corresponding warmed-up gas product, is passed through the cold store and back to the cold end of the main heat exchanger, and is combined again with the here still cryogenic gas product. A corresponding pump or a compressor with an aftercooler (blower) may be used for example for this purpose. The explained variant of the process according to the invention has the advantage that a medium that is at a comparatively low pressure, for example of 1.5 bar, can be used both for cooling down and for warming up the cold storage unit. A corresponding cold storage unit therefore only has to be designed for such low pressures.

It is however also possible in the first operating mode to pass a fraction of the feed air through the cold storage unit for cooling-down purposes and a fraction through at least one portion of the main heat exchanger for cooling-down purposes. Corresponding air is compressed at least to a pressure of a high-pressure column of a corresponding distillation column system, which is for example at 6 bar. The cold storage unit and the cold store or stores installed in it must therefore be designed for corresponding pressures.

In this case, it may also be envisaged, as explained above, to use the mentioned cryogenic gas product from the low-pressure column for cooling down the cold storage unit in the third operating mode, the cold storage unit then having to be designed for operating at different pressures.

It may also be envisaged to pass the entire feed air through at least one portion of the main heat exchanger in the first operating mode and cool it down therein. A fraction of the feed air cooled down in the main heat exchanger may be branched off, recycled through the cold storage unit and passed to the warm end of the main heat exchanger, where it is combined again with the feed air. In this way, a fraction of the cooled-down feed air is always used for cooling down the cold storage unit. A corresponding blower may also be used in this case. This variant of the process according to the invention makes it possible in the first and third operating modes to pass correspondingly higher-compressed air through the cold store, which in this case only has to be designed for operating at one pressure, though higher, for example 6 bar. Alternatively, it may also be envisaged in the third operating mode to pass the entire feed air through at least one portion of the main heat exchanger and cooled the cold store with the other fluid, as already mentioned.

An air separation plant according to the invention for producing an air product is designed for compressing feed air altogether in a main air compressor and thereafter partly recompressing it in a booster air compressor and cooling the feed air down and subsequently entirely or partially feeding it into a distillation column system, said plant being provided with means that are designed for feeding the feed air in a first air feeding amount into the distillation column system in the first operating mode and in this system using the feed air to produce a liquid intermediate product in a first amount of intermediate product, and of the amount of intermediate product, storing one fraction in a liquid form in a storage amount in a liquid storage unit, warming up a further fraction under pressure in a first amount of product in the main heat exchanger and providing it as the air product. These means are also designed for feeding the feed air in a third feeding air amount into the distillation column system in a third operating mode and in this system using the feed air to produce a liquid intermediate product in a third amount of intermediate product, removing the liquid intermediate product stored in the first operating mode in a removal amount from the liquid storage unit in the third operating mode and combining it with the third amount of intermediate product to form a total amount and warming this up in a third amount of product under pressure in the main heat exchanger and providing it as the air product.

According to the invention, the air separation plant is designed for providing the first air feeding amount as greater than the third air feeding amount and in the first operating mode extracting heat from the feed air both in a cold storage unit that is cooled down in the third operating mode and comprises at least one cold store and in the main heat exchanger, and not to pass the first and third amounts of product through the cold storage unit.

A corresponding separation plant advantageously comprises means that are designed for carrying out a process in any of the embodiments of the invention that are explained above and below.

The invention is explained more specifically below with reference to the accompanying drawings, which show preferred embodiments of the invention in comparison with the prior art.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an air separation plant not according to the invention in the form of a process flow diagram.

FIGS. 2A to 2C show an air separation plant in the form of process flow diagrams.

FIGS. 3A to 3C show an air separation plant according to one embodiment of the invention in the form of process flow diagrams.

FIGS. 4A to 4C show an air separation plant according to one embodiment of the invention in the form of process flow diagrams.

FIGS. 5A to 5C show an air separation plant according to one embodiment of the invention in the form of process flow diagrams.

FIGS. 6A to 6C show an air separation plant according to one embodiment of the invention in the form of process flow diagrams.

In the figures, elements that correspond to one another are indicated by identical designations and, for the sake of overall clarity, are not newly explained in all cases.

DETAILED DESCRIPTION OF THE DRAWINGS

In FIG. 1, an air separation plant is represented in the form of a simplified, schematic process flow diagram. The air separation plant comprises a main heat exchanger 10 and a rectification unit 20, which is shown separately merely for purposes of illustration.

In the main heat exchanger unit 10, feed air (AIR) in the form of a stream a is sucked in by way of a main air compressor 11 (MAC) represented in a simplified form, cooled in a pre-cooling unit 12 and purified in a purifying unit 13.

A partial stream b (FEED) of the compressed, cooled and purified stream a is fed on the warm side to a main heat exchanger 14 and removed from it on the cold side. By contrast, a further partial stream c of the compressed, cooled and purified stream a is initially fed for recompression to a booster air compressor 15 (BAC).

Once again, a partial stream d (JT-AIR, the so-called throttle stream) of the partial stream c is recompressed in the booster air compressor to a booster air compressor final pressure, fed on the warm side to the main heat exchanger 14 and removed from it on the cold side.

By contrast, a further partial stream e (TURB, the so-called turbine stream) of the partial stream c is removed from the booster air compressor 15 at a booster air compressor intermediate pressure, compressed further in a turbine-driven compressor 16 (booster), fed on the warm side to the main heat exchanger 14, removed from it at intermediate temperature and expanded in an expansion turbine coupled to the turbine-driven compressor 16. The turbine stream e is combined in the example with the partial stream b to form a collective stream f (here referred to from now on as FEED).

The invention may be used in an air separation plant of the specific configuration illustrated here, but it is also suitable for example for air separation plants with so-called injection turbines, which feed compressed air into the low-pressure column 22 (see below). So-called Lachmann turbines may be used for example for this (cf. for example EP 2 235 460 A1). Processes with a so-called PGAN turbine, which expand a pressurized oxygen stream, are also known in principle to a person skilled in the art.

The provision of a throttle stream d makes the internal compression of liquid intermediate products possible in particular, by contrast, the provision of a turbine stream e influences the cold balance and makes the removal or intermediate storage of greater amounts of liquid air products or intermediate products possible, as explained and described in the cited specialist literature. Put in simple terms, the amount of the throttle stream d correlates with the amount of the internally compressed liquid intermediate products that is to be evaporated (see below); the amount of the turbine stream e correlates with the amount of liquid air products or liquid intermediate products to be formed altogether, which are removed from the air separation plant in a liquid form or are (intermediately) stored in a liquid form.

In the rectification unit 20, the collective stream f (FEED) is fed into the lower region of a high-pressure column 21, which is designed as part of a double column and is in heat-exchanging connection with a low-pressure column 22 by way of a main condenser 23. After expansion in the liquid expander 24 comprising a generator and/or an expansion valve, the throttle stream d (JT-AIR) is likewise fed into the high-pressure column 21 above the collective stream f.

In the high-pressure column 21, a liquid, oxygen-enriched sump product is obtained, which is drawn off out of the sump of the high-pressure column 21 as stream g, passed through a counter-current subcooler 25 and fed into the low-pressure column 22 at a suitable height. In the high-pressure column 21, a gaseous, nitrogen-rich head product is obtained, which is drawn off from the head of the high-pressure column 21 and a fraction of which can be passed as gaseous nitrogen pressurized product (PGAN) to the periphery of the plant. A further fraction of the gaseous, nitrogen-rich head product drawn off from the head of the high-pressure column 21 is liquefied in the main condenser 23, a fraction thereof is returned to the high-pressure column 21 as reflux, a fraction thereof is passed as liquid pressurized nitrogen product (PLIN) to the periphery of the plant or stored in a liquid form, a fraction thereof is passed as stream h through the counter-current subcooler 25 and passed as reflux to the low-pressure column 22, and a fraction thereof is increased in pressure in a liquid form as stream i by means of a pump 26 (this is the internal compression mentioned).

After dividing into two partial streams, the stream i (ICLIN) is vaporized in the main heat exchanger 14 and passed in the form of two gaseous pressurized nitrogen products (ICGAN1, ICGAN2, referred to herein as internal compression products) at different pressure levels to the periphery of the plant. The division into two partial streams before the vaporization in the main heat exchanger 14 is not absolutely necessary; it is also possible for just one corresponding internal compression product to be formed.

Directly underneath the feeding-in point of the throttle stream d into the high-pressure column 21, a liquid stream k is drawn off out of the column and, in the same way as a further stream 1, that is drawn off out of the high-pressure column 21, is passed through the counter-current subcooler 25 and fed into the low-pressure column 22 at a suitable height.

In the low-pressure column 22, a liquid, oxygen-rich sump product is obtained as an intermediate product, which is drawn off out of the sump of the low-pressure column 22, which at the same time represents the evaporation space of the main condenser 23, as stream m1. The first part thereof in the form of a stream m2 is increased in pressure in a liquid form by means of a pump 28 (once again internal compression). In the example shown, after dividing into two partial streams, the stream m2 (ICLOX) is also vaporized in the main heat exchanger 14 and passed in the form of gaseous pressurized oxygen products (HP-GOX, MP-GOX, once again internal compression products) at different pressure levels to the periphery of the plant. Once again, the division into two partial streams before the vaporization in the main heat exchanger 14 is not necessary; it is also possible for just one internal compression product to be formed.

A second part of the sump product m1 is introduced by way of line m3 into a liquid oxygen tank 27. It may be completely or partially passed to the periphery of the plant as a liquid oxygen product (LOX). The rest is stored in a liquid form. When needed, part of the content of the tank can be pumped back into the sump of the low-pressure column 22 by way of pump 121 and line 120.

Also obtained in the low-pressure column 22 is a gaseous, nitrogen-rich head product, which can be drawn off from the head of the high-pressure column 22 in the form of the stream n (GAN), passed through the counter-current subcooler 25, warmed up in the main heat exchanger 14 and passed to the periphery of the plant. From the head of the low-pressure column 22 or from a liquid retention device arranged there, a liquid, nitrogen-rich stream o may be drawn off and, at least in a first part, internally compressed as a further nitrogen-rich liquid 110 as an alternative or in addition to the stream i, in that it is brought to an increased pressure in a liquid form in the pump 112 and subsequently passed by way of line i to the main heat exchanger 14. The rest flows by way of line 113 into a liquid nitrogen tank 42. It may be entirely or partially passed to the periphery of the plant as a liquid nitrogen product (LIN). The rest is stored in a liquid form. An impure nitrogen product (UN2) may be removed from the low-pressure column 22 as stream p, passed through the counter-current subcooler 25, warmed up in the main heat exchanger 14 and used as a so-called residual gas (REST) for operating the pre-cooling device 12 and/or the purifying device 13.

A part 130 of the liquid air in line k is introduced into a liquid air tank 44. Liquid air 134 from the low-pressure column 22 may also be introduced into the liquid air tank 44. The liquid air may be introduced into the low-pressure column 22 by way of a pump 131 and line 133.

In the air separation plant represented in FIG. 1, various liquid intermediate products are produced from air:

The nitrogen-rich liquid of the stream i (ICLIN) from the high-pressure column 21, or to be more precise from the liquefaction space of the main condenser 23, is internally compressed and evaporated (vaporized) in the main heat exchanger 14 to form the internal compression products ICGAN1 and ICGAN2.

The oxygen-rich liquid of the stream m (ICLOX) from the sump of the low-pressure column 22 is internally compressed and evaporated in the main heat exchanger 14 to form the internal compression products HP-GOX and MP-GOX.

The further oxygen-rich liquid 110 from the head of the low-pressure column, which is internally compressed as an alternative or in addition to the stream i.

Liquid air 130/134 from line k or the corresponding portion of the low-pressure column 22.

In the process of FIG. 1, the liquid tanks 112, 27 and 132 form the liquid storage unit. In the same way, an air separation plant may also produce further liquid intermediate products from air, which are evaporated (in the main heat exchanger 14 or in some other way) to form gaseous air products. Internal compression is not absolutely necessary. Liquid intermediate products may also be for example liquid air or liquid argon.

In FIGS. 2A to 2C, an air separation plant is represented in the form of simplified process flow diagrams, which show three operating modes. The air separation plant respectively represented comprises the main heat exchange unit 10 already described above and the rectification unit 20 already explained above. Both are shown in a greatly simplified form.

Furthermore, FIGS. 2A and 2C show only a selection of the streams a to p represented in FIG. 1, to be specific the partial stream b (FEED), the throttle stream d (JT-AIR), the turbine stream e (TURB, not shown here as combined with the partial stream b to form the collective stream f), the internally compressed stream m (ICLOX, here only evaporated in the main heat exchanger 14 to form a single internal compression product, HP-GOX) and the stream p (UN2, REST).

The air separation plant shown in FIGS. 2A to 2C also comprises a cold storage unit 30 with one or more cold stores 31 and a liquid storage unit 40 with one or more storage tanks 41 to 44, for example a liquid oxygen tank 41, a liquid nitrogen tank 42, a liquid argon tank 43 and/or a liquid air tank 44. Not all of the storage tanks 41 to 44 have to be present.

The drawings specifically show the following operating modes:

FIG. 2c : First operating mode—putting into storage

FIG. 2a : Second operating mode—cold store is neither charged or discharged

FIG. 2b : Operating mode—taking out of storage

In the third operating mode, shown in FIG. 2A, the cold storage unit 30 and the liquid storage unit 40 are not in operation, as illustrated by crossed-through flow paths. The operating mode shown in FIG. 2A corresponds to the normal operation of a conventional air separation plant, not according to the invention. In respect of the actual operation of the store, liquid may also be removed from the liquid storage unit as an end product in the third (or in any other) operating mode if there is a demand for it.

In the operating mode shown in FIG. 2A, no liquid intermediate products are stored in the example shown, though liquid intermediate products are produced, being evaporated in the main heat exchanger 14 after internal compression (illustrated here by the example of the internally compressed stream m, ICLOX, but also possible for further liquid intermediate products). The cold management is therefore only illustrated here on the basis of the evaporation of the stream m (ICLOX) to form the corresponding internal compression product (HP-GOX).

Let us assume that an air separation plant is designed for example for providing about 40 000 standard cubic meters per hour of the internal compression product (HP-GOX, or a sum of two or more internal compression products, see HP-GOX and MP-GOX in FIG. 1). Corresponding to the stream m, this amount is denoted in FIG. 2A by M. The air of the stream a (AIR) to be compressed by the main air compressor 11 (see FIG. 1) is typically five to six times the amount M, in the example therefore about 200 000 standard cubic meters per hour. The amount of the throttle stream d (JT-AIR), denoted in FIG. 2A by D, is for its part typically approximately two times the amount M, in the example therefore about 75 000 standard cubic meters per hour. The amount of the turbine stream e (TURB), denoted in FIG. 2A by E, may be assumed for example to be about 65 000 standard cubic meters per hour. The amount of air to be fed into the booster air compressor 15 (booster air compressor amount) (see FIG. 1) of the partial stream c (formed from the turbine stream d and the throttle stream e, see FIG. 1) therefore corresponds in this case to D+E, and therefore is about 140 000 standard cubic meters per hour. The amount B of the stream b is based directly on the amount of their products to be produced and is for example about 60 000 standard cubic meters per hour.

In the operating mode shown in FIG. 2B, which is carried out in times when there is a shortage of electric power (referred to within the scope of this application as the third operating mode), the cold store 31 of the cold storage unit 30 must be in the warmed-up state and a liquid intermediate product must be stored in one or more storage tanks 41 to 44 of the liquid storage unit 40. The required warming up of the cold store 31 of the cold storage unit 30 and the likewise required storage of the liquid intermediate product in one or more storage tanks 41 to 44 of the liquid storage unit 40 take place in the (first) operating mode, explained below in relation to FIG. 2C, and in times when there is a surplus of electric power.

The operation is illustrated once again below on the basis of the use of liquid oxygen as an intermediate product, which is assumed to be stored in the liquid oxygen tank 41. As already emphasized above, the air separation plant may however also be operated by using any other desired liquid intermediate products.

In the third operating mode, shown in FIG. 2B, the air separation plant continues to be operated and supplies corresponding consumers; in addition, however, liquid oxygen is removed from the liquid oxygen tank 41 in the form of a stream q in a removal amount Q. However, no liquid intermediate products are stored any longer.

If the air separation plant is intended to continue providing the same amount of product M of the internal compression product or products as in the operating mode according to FIG. 2A, for example the about 40 000 standard cubic meters per hour mentioned in the example above, the amount of liquid oxygen to be formed as an intermediate product in the air separation plant or the rectification unit 20 itself may be reduced by the removal amount Q from the liquid oxygen tank 41. If the removal amount Q is for example 10 000 standard cubic meters per hour, the air separation plant or the rectification unit 20 therefore only has to contribute about a further 30 000 standard cubic meters per hour itself to the stream m during the operating mode shown in FIG. 2B. The amount of intermediate product and the air feeding amounts to be fed altogether into the rectification unit 20 are reduced correspondingly.

The air of the stream a (AIR) to be compressed by the main air compressor 11 (see FIG. 1) is also reduced by about 25%, i.e. from about 200 000 standard cubic meters per hour (see explanations relating to FIG. 2A) to about 150 000 standard cubic meters per hour. Consequently, the power consumption for the main air compressor 11 is reduced by about 25%.

Since the entire amount M of the stream m of about 40 000 standard cubic meters per hour still has to be evaporated in the main heat exchanger 14, altogether a sufficient amount D of the throttle stream d (JT-AIR) still has to be provided, in the present example therefore about 75 000 standard cubic meters per hour. In the example shown, however, only a part of the amount D has to be provided by the booster air compressor 15 (see FIG. 1) itself, because a further part, in the example shown in the form of the stream r, can be circulated in an amount R through the cold store 31 of the cold storage unit 31 by means of a pump 32. As a result, the cold store 31 is cooled down. The amount of air of the throttle stream d (JT-AIR) to be provided by the booster air compressor 15 is thereby reduced initially by the amount R, for example by an amount R of about 11 500 standard cubic meters per hour, as illustrated in FIG. 2B by D-R.

Because at the same time a small amount of cold is required on account of the reduced production of the stream m (ICLOX), that is to say of the liquid intermediate product, by the air separation plant itself, in the third operating mode, shown in FIG. 2B, the turbine-operated compressor 16 or its expansion turbine may be switched off or at least greatly throttled. The amount E of the turbine stream e (TURB) is reduced as a result to a permissible minimum. The amount of air of the turbine stream e likewise to be provided by the booster air compressor 15 is thereby reduced.

Altogether, the air of the partial stream c (formed from the throttle stream d and the turbine stream e, see FIG. 1) that is to be compressed by the booster air compressor 15 is reduced by about 8%, i.e. from about 140 000 standard cubic meters per hour (see explanations relating to FIG. 2A) to about 128 500 standard cubic meters per hour. Consequently, the power consumption for the booster air compressor 15 is also reduced by about 8%.

In the operating mode shown in FIG. 2C, which is carried out in times when there is a surplus of electric power and is referred to here as the first operating mode, the cold store 31 of the cold storage unit 30 must be in the cooled-down state and there must be capacity for storing a corresponding liquid intermediate product in one or more storage tanks 41 to 44 of the liquid storage unit 40. The cooling down of the cold store 31 of the cold storage unit 30 and the removal of a liquid intermediate product from one or more storage tanks 41 to 44 of the liquid storage unit 40 in times when there is a shortage of electric power has been explained in relation to the third operating mode, shown in FIG. 2B.

If, here too, the air separation plant is intended to continue providing the same amount M of the internal compression product or products as in the operating mode according to FIGS. 2A and 2B, for example the about 40 000 standard cubic meters per hour mentioned in the above example, but at the same time a storage amount S, for example about 10 000 standard cubic meters per hour, of a produced intermediate product is to be put into storage in the liquid oxygen tank 41 in the form of the stream s, the amount of the intermediate product formed in the air separation plant must increase correspondingly to about 50 000 standard cubic meters per hour. The air feeding amount into the rectification unit for the distillation column system is increased.

The air of the stream a (AIR) to be compressed in this case by the main air compressor 11 (see FIG. 1) increases correspondingly, in the example therefore from about 200 000 standard cubic meters per hour (see explanations relating to FIG. 2A) to about 250 000 standard cubic meters per hour, and consequently by about 25%. The same applies corresponding to the power consumption. For the evaporation of the liquid intermediate product or products to form the internal compression product or products, about 75 000 standard cubic meters per hour of the throttle stream d (JT-AIR) continues to be required in the heat exchanger 14 itself. The amount D of the stream d is then increased overall however, in order to cover the increased demand, in the example to about 86 500 standard cubic meters per hour. Part of this is however passed through the cold store 31 of the cold storage unit 30 cooled down, for example an amount T in the form of the stream t of 11 500 standard cubic meters per hour. In this case, only the remaining and usual (cf FIGS. 2A and 2B) 75 000 standard cubic meters per hour are passed through the main heat exchanger 14. The amount of the throttle stream can therefore be given as D+T.

As a result of the additional amount of cold removed from the cold store 31 of the cold storage unit 30, the amount E of the throttle stream e (TURB) can remain constant, or possibly be increased to a maximum achievable in the plant without the use of further expansion turbines, for example to about 11 500 standard cubic meters per hour. The amounts from throttle stream d and turbine stream e, D and E, give the amount of the partial stream c that is to be compressed by the booster air compressor 15 (formed from the throttle stream d and the turbine stream e) as about 151 500 standard cubic meters per hour.

Altogether, a significantly reduced power consumption is achieved in the third operating mode according to FIG. 2B, whereas a significantly increased power consumption is achieved in the first operating mode according to FIG. 2C. In the first operating mode according to FIG. 2C, a liquid intermediate product, which is used in the third operating mode according to FIG. 2B, is in this case stored. The operating modes represented in FIGS. 2B and 2C can be realized without providing complex additional machines, just by the use of simple cold stores.

The following table provides once again an overview of the amounts of air respectively to be compressed in the main compressor and the booster air compressor and the amount of the turbine stream, which are in each case given in standard cubic meters per hour. The resultant differences between the respective minimum and maximum amounts can be overcome without any problem by conventional machines.

Operating mode Main compressor Booster air compressor FIG. 2A 200 000 140 000 FIG. 2B (first) 150 000 128 500 FIG. 2C (second) 250 000 151 500

As can be seen by viewing FIGS. 2B and 2C together, the cold storage unit 30 used here or the cold store or stores used in the cold storage unit 30 must be able to operate under the pressure of the throttle stream d.

For this purpose, high-pressure vessels designed for corresponding pressures must be provided, which may possibly prove to be expensive.

In FIGS. 3A to 3C, an air separation plant according to one embodiment of the invention is represented in the form of simplified flow diagrams, again the three operating modes being shown. Again, in FIG. 3A normal operation without storage or removal of liquid storage products is illustrated. In FIG. 3B, a third operating mode, which is carried out during times when there is a shortage of electric power and involving removal of a liquid intermediate product from the liquid storage unit 40 or the liquid tank 41, is shown and, in FIG. 3C, a first operating mode, which is carried out during times when there is a surplus of electric power and involving putting a liquid intermediate product into storage in the liquid storage unit 40 or the liquid tank 41.

The cold storage unit 30 is illustrated here by two cold stores 33 and 34, which are respectively charged with partial streams. The cold store 34 is flowed through by streams that are previously and subsequently passed through the main heat exchanger 14. The provision of the cold store 34 serves for balancing the main heat exchanger 14.

Furthermore, the two cold stores 33 and 34 are flowed through by the stream p (UN2), that is to say an impure nitrogen product that is at the pressure of the low-pressure column 21, therefore for example at 1.5 bar, and cooled down according to the third operating mode that is illustrated in FIG. 3B. The effect thereby brought about is that, by contrast with the operating mode illustrated in FIG. 3A, the amount of the stream p passed through the two cold stores 33 and 34 no longer has to be warmed up in the main heat exchanger 14, and therefore the main heat exchanger 14 has a corresponding additional (released) evaporation capacity.

If it is again assumed that, in the operating modes illustrated in FIGS. 3A and 3B, the same amount M of the internal compression product or products is to be provided in the form of the stream m and evaporated, this evaporation capacity of the main heat exchanger 14 that is additionally available in the operating mode according to FIG. 3B can be used for this. The amount D of the throttle stream d (JT-AIR) can be correspondingly reduced, for example by about 15 000 standard cubic meters per hour if about 12 000 standard cubic meters per hour are passed through the cold store 33 and about 10 000 standard cubic meters per hour are passed through the cold store 34. As a result of the reduced amount D of the throttle stream d (JT-AIR) and the, here too, reduced amount E of the turbine stream e (TURB, see explanations relating to FIG. 2B for reasons), the required power of the booster air compressor 15 is also reduced considerably here, for example as above to 125 000 standard cubic meters per hour.

Because, here too, a removal amount Q of a liquid intermediate product is removed from the liquid tank 41 of the liquid storage unit 40 and not produced in the rectification unit 20 itself, the amount of the feed air to be compressed by the main air compressor 2 in the form of the stream a is reduced, as explained in relation to FIG. 2B.

In the first operating mode, which is illustrated in FIG. 3C and, as mentioned, is carried out during times when there is a surplus of electric power, again the same amount M of the internally compressed, liquid intermediate product is provided and evaporated in the main heat exchanger 14 to form the corresponding air product. At the same time, a storage amount S of a liquid intermediate product provided by the rectification unit 20 in the form of the stream s is stored in the liquid tank 41 of the liquid storage unit 40. This means that a greater amount of cold is to be provided in the first operating mode according to FIG. 3C in comparison with the third operating mode according to FIG. 3B. This is provided by the expansion of a correspondingly greater amount E of the turbine stream e. Consequently, an increased power of the booster air compressor 15 is required in comparison with the operating mode illustrated in FIG. 3B (see explanations relating to FIG. 2C for reasons).

In the first operating mode according to FIG. 3C, the entire stream p (UN2, impure nitrogen) is passed through the main heat exchanger 14. The required evaporation capacity of the main heat exchanger 14 consequently increases correspondingly. This required increased evaporation capacity is covered by the provision of a correspondingly increased amount D of the throttle stream d (JT-AIR). Also as a result, the required power of the booster air compressor 15 increases to a corresponding extent, for example by about 15 000 standard cubic meters per hour in comparison with the operating mode shown in FIG. 3A and by about 30 000 standard cubic meters per hour in comparison with the operating mode shown in FIG. 3B. For the additional provision of the storage amount S of the liquid intermediate product, which is to be put into storage in the liquid store 41 in the form of the stream s, the provision of a correspondingly increased amount of compressed air by the main air compressor 2 is required. However, in the first operating mode according to FIG. 3C, a stream b formed from this is only partly cooled down in the main heat exchanger 14, whereas another part is cooled down in the cold stores 33 and 34 of the cold storage unit 30. The required power of the main air compressor 2 consequently increases correspondingly, without overloading the capacity of the main heat exchanger 14.

In the air separation plant illustrated in FIGS. 3A to 3C, the cold stores 33 and 34 are charged with the stream p (UN2, impure nitrogen) at the pressure level of the low-pressure column 22, that is to say as mentioned for example 1.5 bar, in the third operating mode that is shown in FIG. 3B. By contrast with this, in the first operating mode, shown in FIG. 3C, the stream b is passed through the cold stores 33 and 34 at correspondingly high pressure, to be specific at the pressure level of the low-pressure column of for example 6 bar. This means that the cold stores 33 and 34 have to be designed for the correspondingly higher pressure level, and so they are cold stores that have to be designed both for operation at a low pressure level and for operation at a high pressure level.

In FIGS. 4A to 4C, an air separation plant according to one embodiment of the invention is represented in the form of simplified process flow diagrams, which again show the three operating modes mentioned. Once again, in FIG. 4A normal operation without storage or removal of liquid intermediate products is illustrated; in FIG. 4B, a third operating mode, which is carried out during times when there is a shortage of electric power and involving removal of a liquid intermediate product from the liquid storage unit 40 or the liquid tank 41 and, in FIG. 4C, a first operating mode, which is carried out during times when there is a surplus of electric power and involving putting a liquid intermediate product into storage in the liquid storage unit 40 or the liquid tank 41.

The third operating mode represented in FIG. 4B corresponds to the third operating mode represented in FIG. 3B, i.e. a stream p (UN2, impure nitrogen) is partially passed through the main heat exchanger 14 and partially passed through the cold stores 33 and 34 of the cold storage unit 30.

According to the first operating mode illustrated in FIG. 4C, however, the stream p (UN2, impure nitrogen) is also used for heating up the cold stores 33 and 34 of the cold storage unit 30. The stream p is in this case partly compressed by means of a blower unit 35 on the warm side of the main heat exchanger 14 and passed through the cold stores 33 and 34 of the cold storage unit 30. Correspondingly, cooled-down streams are combined with the stream p on the cold side of the main heat exchanger 14, so that in this way altogether an increased evaporation capacity is required in the main heat exchanger 14. This is again covered by an increase in the amount D of the throttle stream d (JT-AIR).

Once again, as explained above in relation to FIG. 3C, the amount E of the turbine stream e is increased. The effects brought about according to the first operating mode shown in FIG. 4C consequently correspond to those of the first operating mode according to FIG. 3C. However, because the cold stores 33 and 34 in both operating modes, i.e. in the third operating mode according to FIG. 4B and the first operating mode according to FIG. 4C, streams at low pressure are respectively passed through the cold stores 33 and 34, they only have to be designed for correspondingly lower pressures.

In FIGS. 5A to 5C, an air separation plant according to one embodiment of the invention is represented in the form of simplified process flow diagrams, which again show the three operating modes in the same arrangement.

According to the third operating mode illustrated in FIG. 5B, which is carried out in times when there is a shortage of electric power, part of the stream b (FEED) is recycled through the cold stores 33 and 34 of the cold storage unit 30, for which purpose a corresponding blower unit 36 is used. The fact that the streams recycled through the cold stores 33 and 34 of the cold storage unit 30 can be removed from the main heat exchanger 14 on the cold side, or at corresponding intermediate temperatures, means that these cold stores 33 and 34 can be cooled down. The amount of air of the stream b that is recycled through the cold stores 33 and 34 is for example about 25 000 standard cubic meters per hour. The amount of production of the rectification unit 20 is again reduced on account of the removal of the removal amount Q of the stream q of the liquid intermediate product, so that a correspondingly lower amount D of the stream d is also required. The amount M of the internally compressed intermediate product (ICOLX) that is to be evaporated in the form of the stream m once again remains the same; the required evaporation capacity is provided by additionally putting a certain amount of cold into storage in the cold storage units 33 and 34. Again, the turbine stream e or the amount E can be throttled to a minimum, because no liquid intermediate products are stored.

During the first operating mode illustrated in FIG. 5C, the additional amount of cold for providing the greater amount B here of the stream b is covered from the cold stores 33 and 34 of the cold storage unit 30.

In FIGS. 6A to 6C, an air separation plant according to one embodiment of the invention is represented in the form of simplified process flow diagrams, which again show three operating modes in the same arrangement. It differs from the previous exemplary embodiments essentially in that, in the first operating mode (FIG. 6C), gaseous pressurized oxygen HP-GOX is cooled down in the cold store 33 and, in the third operating mode (FIG. 6B), ICLOX is evaporated and warmed up in the cold store 31. 

1. A process for producing an air product in an air separation plant in which feed air, which is altogether compressed in a main air compressor and thereafter partly recompressed in a booster air compressor, is cooled down and subsequently entirely or partially fed into a distillation column system, the process comprising, in a first operating mode feeding the feed air in a first air feeding amount into the distillation column system, and in this system using the feed air to produce a liquid intermediate product in a first amount of intermediate product, of the first amount of intermediate product, storing at least one fraction in a liquid form in a storage amount in a liquid storage unit, warming up a further fraction of the first amount of intermediate product or of another amount of liquid intermediate product under pressure in a first amount of product in the main heat exchanger and providing it as the air product and allowing a cold storage unit with at least one cold store to be flowed through by a first process stream, the cold store being warmed up and the first process stream being cooled down, and in a second operating mode feeding the feed air in a second air feeding amount into the distillation column system and in this system using the feed air to produce a liquid intermediate product in a second amount of intermediate product, the cold storage unit not being flowed through, in a third operating mode feeding the feed air in a third air feeding amount into the distillation column system and in this system once again using the feed air to produce a liquid intermediate product in a third amount of intermediate product, the first air feeding amount being greater than the third air feeding amount, removing the liquid intermediate product stored in the first operating mode in a removal amount from the liquid storage unit and combining it with the third amount of intermediate product to form a total amount, which is warmed up under pressure in the main heat exchanger in a third amount of product and provided as the air product, and allowing the cold storage unit to be flowed through by a second process stream, the cold store being cooled down, the second process stream being warmed up.
 2. The process as claimed in claim 1, in which the part of the feed air that is recompressed in the booster air compressor is recompressed there in a booster air compressor amount, the booster air compressor amount being greater in the first operating mode than in the third operating mode.
 3. The process as claimed in claim 2, in which, at least in the first operating mode, part of the booster air compressor amount is cooled down in a turbine stream amount to a temperature level that lies above the liquefaction temperature of nitrogen, and is expanded in an expansion machine, and in which part of the booster air compressor amount is cooled down in a throttle stream amount to a temperature level that lies below the liquefaction temperature of nitrogen, and is expanded.
 4. The process as claimed in claim 3, in which the sum of the turbine stream amount and the throttle stream amount is greater in the first operating mode than in the third operating mode.
 5. The process as claimed in claim 3, in which, after expansion, the throttle stream amount and the turbine stream amount are fed into the distillation column system as part of the air feeding amount.
 6. The process as claimed in claim 1, in which part of the feed air that is not compressed in the booster air compressor is expanded by way of an expansion turbine into a low-pressure column of the distillation column system of the air separation plant.
 7. The process as claimed in claim 1, in which a fraction of a cryogenic gas product removed from the distillation column system, not in the form of the first and/or third amount of intermediate product, is passed through the cold storage unit in the cryogenic state in the third operating mode to cool the unit down.
 8. The process as claimed in claim 7, in which the cryogenic gas product is warmed up completely in the main heat exchanger, a fraction of the warmed-up gas product subsequently being passed through the cold storage unit to warm the unit up.
 9. The process as claimed in claim 1, in which in the first operating mode part of the feed air is passed through the cold storage unit for cooling-down purposes and part through at least one portion of the main heat exchanger.
 10. The process as claimed in claim 1, in which in the third operating mode the entire feed air is passed through at least one portion of the main heat exchanger and cooled down therein, a fraction of the cooled-down feed air being used thereafter for cooling down the cold storage unit.
 11. The process as claimed in claim 1, in which in the third operating mode the entire feed air is passed through at least one portion of the main heat exchanger.
 12. An air separation plant for producing an air product, which is designed for compressing feed air altogether in a main air compressor and thereafter partly recompressing it in a booster air compressor and cooling the feed air down and subsequently entirely or partially feeding it into a distillation column system, said plant being provided with means that are designed for in a first operating mode feeding the feed air in a first air feeding amount into the distillation column system, and in this system using the feed air to produce a liquid intermediate product in a first amount of intermediate product, and of the first amount of intermediate product, storing at least one fraction in a liquid form in a storage amount in a liquid storage unit, warming up a further fraction of the first amount of intermediate product or of another amount of liquid intermediate product under pressure in a first amount of product in the main heat exchanger and providing it as the air product and allowing a cold storage unit with at least one cold store to be flowed through by a first process stream and warmed up, the first process stream being cooled down, and in a second operating mode feeding the feed air in a second air feeding amount into the distillation column system and in this system using the feed air to produce a liquid intermediate product in a second amount of intermediate product, the cold storage unit not being flowed through, in a third operating mode feeding the feed air in a third air feeding amount into the distillation column system and in this system once again using the feed air to produce a liquid intermediate product in a third amount of intermediate product, the first air feeding amount being greater than the third air feeding amount, removing the liquid intermediate product stored in the first operating mode in a removal amount from the liquid storage unit and combining it with the third amount of intermediate product to form a total amount and warming it up under pressure in the main heat exchanger in a third amount of product and providing it as the air product, and allowing the cold storage to be flowed through by a second process stream and cooled down, the second process stream being warmed up. 